The rheological behavior of 6818 high temperature epoxy resin system for resin transfer molding process (RTM) was studied, according to the differential scanning calorimetry analysis (DSC) and viscosity experiments. The curing process of 6818 resin system was determined by extrapolation. A rheological model based on dual-Arrhenius equation was established. The curve tallied exactly with the experimental results. The results showed that the viscosity of the 6818 resin was under 200 mPa·s within the temperature range from 80℃ to 100℃, and the viscosity maintaining time more than 12 hours. The model could reflect the viscosity change of 6818 resin and predict the RTM process window of the resin system.